Dual-active-bridge (DAB) direct current to direct current (DC-DC) converters are widely used in high power applications, such as variable-speed generators, electrical vehicles, switch-mode electronics, battery stores, alternative energy harnessing, renewables integration, and so on. The DAB DC-DC converter includes an H-bridge on each of the input and output sides of a transformer. Power transmission between the input and output sides depends on the leakage inductance of the transformer. When the DAB DC-DC converter is being started, the voltage at the output side is approximately zero at the beginning. The voltage at the input side is thus applied substantially fully on the leakage inductance of the transformer, which may result in large asymmetrical inrush current in the transformer. The inrush current may be several times of the steady-state current and may damage electric components and/or cause transformer saturation.